Conventionally, a digital process for making a master plate is well known as a method of making stencil master plates for stencil printing. In the digital master plate making method, an original is photoelectrically read by using an image scanner, and a heat sensitive film of a thermal stencil master plate made of thermoplastic resin is perforated in the manner of a dot matrix by selectively and individually driving a plurality of dot-like heat emitting elements of a thermal head.
In the above described digital method of making a master plate, it has been proposed to photoelectrically read a region designating sheet carrying region designating images separately from the original image, and carry out an image makeup function, such as halftone, reversal, outlining (converting characters into outlined characters), and photography mode, on designated regions of the original corresponding to selected region designating images.
Conventionally, the above described image makeup processing was conducted by setting up image makeup functions such as halftone, reversal, outlining and photography mode from a keyboard, and photoelectrically reading region designating images which are drawn on a region designating sheet. By drawing a plurality of region designating images on the region designating sheet, it is possible to designate a plurality of regions for an image makeup function.
However, even when a plurality of regions are defined on an original with the intention of applying makeup functions thereto by drawing a plurality of region designating images on a single region designating sheet, the image makeup functions can be set up with only one kind for each region designating sheet, and it has not been possible to apply a different image makeup function to each of the designated regions.
Therefore, conventionally, when different image makeup functions such as halftone and reversal are to be applied to different parts of an original image, it has been necessary to prepare a region designating sheet carrying region designating images for each different image makeup function, to sequentially set up each image makeup function from a keyboard, and to sequentially read the region designating sheets each carrying different region designating images in the order of setting up the image makeup functions from the keyboard.
In the above described method, however, the user must remember the order of the image makeup functions which he had set up from the keyboard, and must supply each of the region designating sheets to a read out unit in the same order. This procedure is so complicated that the user can make errors. Such errors in the image makeup process can be found only after a test print is made, and this causes wasting of stencil master plates as well as of printing paper.
Further, region designating images displayed on the display unit are line images freely drawn by the user on a region designating sheet, and the touch panel consists of a matrix of switch segments each approximately 1 cm square. Therefore, when a plurality of region designating images are drawn on the region designating sheet close to each other, there is a possibility that two different region designating images may fall on a same square switch segment. In such a case, pressing such a switch segment means an indeterminate instruction, and would not specify a desired one of the region designating images.